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Pieces in a Global Picture

Maryland Research Paints Key Portions of an Earth Science Portrait of Climate Change

Story by Stephen Berberich

Long before modern science, a grizzled farmer, a salty sea captain, or the gray-bearded leader of a wandering tribe may have been able to sense a major weather change coming. Perhaps they faced a long drought, shifting trade winds, or colder winters. They surely thought, "Things seem to be changing."

Today, things are indeed changing. A vast majority of scientists agree that the global climate is warming. And humans clearly have something to do with it. The signs are evident in the skies, the land and the seas. Civilization's exhaust pipes are loading the atmosphere with gases, such as carbon dioxide and methane, adding to a warming greenhouse effect. Vast amounts of land around the globe are being transformed by urbanization, agriculture, logging and other human activities in ways that not only raise local temperatures, but also appear to contribute to the warming of the planet. Arctic Sea ice is melting, and sea levels are rising at apparently increasing rates.

However, much remains uncertain about climate change, including: How much global warming will occur over the next 100 years? How responsible are humans for this warming trend? And, a question that for many people is probably the biggest one: What is going to happen to the weather where I live?

understanding climate cycles

At the University of Maryland, researchers in the Earth System Science Interdisciplinary Center, or ESSIC, are working to develop the scientific understanding and computer models needed to find answers to these and other key questions about climate change. One central part of that effort is the center's work to understand the natural climate cycles such as El Nino that determine climate over shorter time frames.

"We know that as more energy is put into the Earth system through global warming that energy eventually will be projected through and manifested by our planet's natural climate cycles, and it's these cycles that influence regional weather," explains Antonio J. Busalacchi, professor and director of ESSIC. "Improving our understanding of these natural cycles and how they interact will allow us to improve our models of these cycles, which, in turn, improves our modeling of the regional and global impacts of global climate change."

Driven by energy from the sun, climate cycles are a function of the Earth system and the interaction between its four components: atmosphere, oceans, land and living things, says Busalacchi, who chairs the National Academies' Climate Research Committee. "At ESSIC we are learning how the parts of the Earth system couple together. As a result, for the first time we are beginning to appreciate the climate cycles."

The three major research thrusts of the center are studies of (a) climate variability and change, (b) atmospheric composition and processes, and (c) the cycling of carbon through different parts of the Earth system. Every day at ESSIC, nearly 90 faculty, research assistants and graduate students work with collaborators around the world to piece together and analyze data from a variety of sources.

Measurements and observations of recent and on going climate change are obtained from Earth-observing satellites and on-land and at-sea measuring devices. Evidence of past changes in climate comes from ancient rocks, ice cores and rainfall records. ESSIC scientists use this data not only to understand and model cycles, but also to determine how much of our planet's current warming trend is due to long-term climate cycles and how much is caused by human activities.

El Nino Research Heats Up

A major focus for many at ESSIC is understanding the powerful climate cycle that scientists call El Nino/Southern Oscillation.

"The El Nino/Southern Oscillation of El Nino warming and La Nina ocean cooling in the equatorial Pacific is the largest climate signal on the planet," says Busalacchi. "Ocean currents and water temperatures change over a third of the globe during these events, leading to disruptive weather patterns and serious consequences for human populations."

One ESSIC research team recently added a "pinch of sea salt" to models of El Nino. Led by Joaquim Ballabrera, Busalacchi and Ragu Murtugudde, and sponsored by NASA, the team discovered that, months before an El Nino event occurs, changes in the saltiness of surface waters coincide with changes in water temperature in key regions of the western Pacific Ocean.

Because salt and heat affect density and thus the height of the sea, they concluded that monitoring sea levels will significantly improve season-to-season climate predictions.

A Three Partner Boogie

Ten years ago, the Washington Post reported that the "condition known as El Nino is born of a 'dance' between the Pacific Ocean and the tropical wind." Maryland researchers are finding that the climate-changing power of this dance involves not only the atmosphere and the physical conditions of the Pacific Ocean, like temperature and saltiness, but also its marine life.

A recent study by scientists from ESSIC, Dalhousie University in Halifax Canada, and the National Oceanographic and Atmospheric Administration, or NOAA, showed that during El Nino/La Nina events, there is a major disruption of the ocean food chain. The researchers analyzed satellite observations of the tropical Pacific Ocean, surface temperature readings from buoys and deeper water measurements taken by ships. They found that during El Nino there is a decrease in the capacity of eastern Pacific marine life to take up and store carbon--primarily the result of a decrease in phytoplankton production.

"We have found there is a feedback between the lowest levels of the food chain and the physics," explains Busalacchi. "So the biology in the ocean changes how light is absorbed and how the upper part of the ocean is heated."

Since the 1970s, scientists had speculated that an important part of the El Nino equation might be missing. "What is really exciting is that we always had a hard time getting the ocean warming right in March and April," explains Ragu Murtugudde, an associate professor in ESSIC and the Department of Meteorology. "And now we have shown that in fact biology is very crucially controlling this warming season."

Together with other findings, this study also indicates that the largest natural variations of the carbon cycle occur in the cycle of El Nino and La Nina events. During the past decade, scientists and policy makers have intensified their interest in the global movement of carbon, because carbon is a key element in living things, food, energy sources, greenhouse gases and quite possibly climate change.

Seeing the Forest in the Trees

Ruth DeFries, a professor in ESSIC and the Department of Geography, is also interested in the carbon cycle. DeFries investigates the relationship of the land surface, human activities, and physical, chemical and biological processes. In Santa Cruz, Bolivia, a region with one of the world's highest rates of deforestation, DeFries and Lahouari Bounoua of ESSIC/NASA, together with other researchers, have determined that when tropical forests are cut down or when crops are planted in place of native grasslands, the land warms considerably. Average daytime surface temperatures rose by as much as 3.6 degrees F (2 degrees C) where tropical forest species were replaced by crops.

The researchers developed a method to map tree cover continually over extended periods of time using data from NASA's Terra satellite. Their method produces measures of deforestation that are far more accurate than flawed United Nations figures on deforestation, which are a compilation of estimates reported by individual countries.

From the perspective of global climate change, accurately measuring forest cover and deforestation rates is part of a larger goal to figure out how much carbon is "exported" from deforested land. "It is still a matter of estimating," says DeFries. "You can estimate from satellite images how much forest is there and how much carbon is in that biomass. We try to trace how much of the carbon then ends up in the atmosphere, what percentage decays, what percentage burns, what percentage is taken away for furniture [lumber]."

Satellite Science

Landsat images showing progressive deforestation (lighter areas) of tropical dry forest east of Santa Cruz de la Sierra, Bolivia from 1975 to 2000.

One of the most powerful tools used by ESSIC scientists are NASA and NOAA satellites. For example, researchers study El Nino/Southern Oscillation scale climate change with NASA's Topex/Poseidon satellite altimeter, part of an unprecedented tide of new observational satellites. The instrument, built by NASA and the Centre National d'Etudes Spatiales in France can measure sea surface levels to an accuracy of two centimeters from an orbit 1,300 kilometers above the Earth. "It is like sitting in my office at College Park and seeing the tide change on the beach at Jacksonville, Florida," says Busalacchi.

ESSIC deputy director Phil Arkin is leading a team that is reworking models of the global diurnal cycle of precipitation by coupling measures of ocean and atmosphere conditions. The team uses a combination of microwaves from polar orbiting satellites and infrared measurements from geo-stationary satellites (those spinning "in step" with the Earth's spin).

Arkin explains that current rain models are based on more than 100 years of records on precipitation in much of the world. However, Arkin says daily rain patterns and ocean storm tracks in these models are incomplete and sometimes reflect "the wrong flavor of behavior." For example, current climate models "expect" summer thunderstorms in Maryland to start each day as the sun reaches its zenith, at noon or 1 p.m. However, most of the electrical storms actually occur in late afternoon and evening.

ESSIC scientists are also using satellites to improve models of the role water vapor plays in global warming.

Like carbon dioxide, water vapor is a greenhouse gas that traps heat in the atmosphere, as global temperatures rise, more water can be expected to evaporate from the oceans further increasing the amount of water vapor in the atmosphere. However, the size of this "positive water vapor feedback" is a key debate within climate science circles.

In a NASA-funded study published in March, Andrew Dessler, a researcher in ESSIC and the Department of Meteorology, and colleague Ken Minschwaner of the New Mexico Institute of Mining used NASA's UARS satellite to measure water vapor on a global scale. They found that global warming is increasing the amount of water vapor entering the atmosphere. However, their work showed that the amount is not as high as many climate-forecasting computer models have assumed. Their finding suggests some climate forecasts may be overestimating future temperature increases.

"One of the responsibilities of science is making good predictions of the future climate because that's what policy makers use to make their decisions," says Dessler. "This study is another incremental step toward improving those climate predictions."

Understanding Uncertainty

Ultimately, say ESSIC scientists, their work is about improving understanding of the Earth system and the uncertainties associated with climate change.

"They used to say in the 1980's that global warming will raise mean global temperature between 2 to 5 degrees in the next 100 years," says researcher Murtugudde. "We are still in the same range of uncertainty, but we know much more from studies of ice feedbacks, terrestrial limitation feedbacks, land vegetation, land use change, emissions ... everything.

"Our models have gotten better because the science and information is getting better. Hopefully decisions also will be getting better, despite the uncertainty associated with [climate change]."